diff options
Diffstat (limited to 'gdb/nat/fork-inferior.c')
| -rw-r--r-- | gdb/nat/fork-inferior.c | 595 |
1 files changed, 595 insertions, 0 deletions
diff --git a/gdb/nat/fork-inferior.c b/gdb/nat/fork-inferior.c new file mode 100644 index 00000000000..0913409e6dd --- /dev/null +++ b/gdb/nat/fork-inferior.c @@ -0,0 +1,595 @@ +/* Fork a Unix child process, and set up to debug it, for GDB and GDBserver. + + Copyright (C) 1990-2017 Free Software Foundation, Inc. + + This file is part of GDB. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see <http://www.gnu.org/licenses/>. */ + +#include "common-defs.h" +#include "fork-inferior.h" +#include "target/waitstatus.h" +#include "filestuff.h" +#include "target/target.h" +#include "common-inferior.h" +#include "common-gdbthread.h" +#include "signals-state-save-restore.h" +#include <vector> + +extern char **environ; + +/* Default shell file to be used if 'startup-with-shell' is set but + $SHELL is not. */ +#define SHELL_FILE "/bin/sh" + +/* Build the argument vector for execv(3). */ + +class execv_argv +{ +public: + /* EXEC_FILE is the file to run. ALLARGS is a string containing the + arguments to the program. If starting with a shell, SHELL_FILE + is the shell to run. Otherwise, SHELL_FILE is NULL. */ + execv_argv (const char *exec_file, const std::string &allargs, + const char *shell_file); + + /* Return a pointer to the built argv, in the type expected by + execv. The result is (only) valid for as long as this execv_argv + object is live. We return a "char **" because that's the type + that the execv functions expect. Note that it is guaranteed that + the execv functions do not modify the argv[] array nor the + strings to which the array point. */ + char **argv () + { + return const_cast<char **> (&m_argv[0]); + } + +private: + /* Disable copying. */ + execv_argv (const execv_argv &) = delete; + void operator= (const execv_argv &) = delete; + + /* Helper methods for constructing the argument vector. */ + + /* Used when building an argv for a straight execv call, without + going via the shell. */ + void init_for_no_shell (const char *exec_file, + const std::string &allargs); + + /* Used when building an argv for execing a shell that execs the + child program. */ + void init_for_shell (const char *exec_file, + const std::string &allargs, + const char *shell_file); + + /* The argument vector built. Holds non-owning pointers. Elements + either point to the strings passed to the execv_argv ctor, or + inside M_STORAGE. */ + std::vector<const char *> m_argv; + + /* Storage. In the no-shell case, this contains a copy of the + arguments passed to the ctor, split by '\0'. In the shell case, + this contains the quoted shell command. I.e., SHELL_COMMAND in + {"$SHELL" "-c", SHELL_COMMAND, NULL}. */ + std::string m_storage; +}; + +/* Create argument vector for straight call to execvp. Breaks up + ALLARGS into an argument vector suitable for passing to execvp and + stores it in M_ARGV. E.g., on "run a b c d" this routine would get + as input the string "a b c d", and as output it would fill in + M_ARGV with the four arguments "a", "b", "c", "d". Each argument + in M_ARGV points to a substring of a copy of ALLARGS stored in + M_STORAGE. */ + +void +execv_argv::init_for_no_shell (const char *exec_file, + const std::string &allargs) +{ + + /* Save/work with a copy stored in our storage. The pointers pushed + to M_ARGV point directly into M_STORAGE, which is modified in + place with the necessary NULL terminators. This avoids N heap + allocations and string dups when 1 is sufficient. */ + std::string &args_copy = m_storage = allargs; + + m_argv.push_back (exec_file); + + for (size_t cur_pos = 0; cur_pos < args_copy.size ();) + { + /* Skip whitespace-like chars. */ + std::size_t pos = args_copy.find_first_not_of (" \t\n", cur_pos); + + if (pos != std::string::npos) + cur_pos = pos; + + /* Find the position of the next separator. */ + std::size_t next_sep = args_copy.find_first_of (" \t\n", cur_pos); + + if (next_sep == std::string::npos) + { + /* No separator found, which means this is the last + argument. */ + next_sep = args_copy.size (); + } + else + { + /* Replace the separator with a terminator. */ + args_copy[next_sep++] = '\0'; + } + + m_argv.push_back (&args_copy[cur_pos]); + + cur_pos = next_sep; + } + + /* NULL-terminate the vector. */ + m_argv.push_back (NULL); +} + +/* When executing a command under the given shell, return true if the + '!' character should be escaped when embedded in a quoted + command-line argument. */ + +static bool +escape_bang_in_quoted_argument (const char *shell_file) +{ + size_t shell_file_len = strlen (shell_file); + + /* Bang should be escaped only in C Shells. For now, simply check + that the shell name ends with 'csh', which covers at least csh + and tcsh. This should be good enough for now. */ + + if (shell_file_len < 3) + return false; + + if (shell_file[shell_file_len - 3] == 'c' + && shell_file[shell_file_len - 2] == 's' + && shell_file[shell_file_len - 1] == 'h') + return true; + + return false; +} + +/* See declaration. */ + +execv_argv::execv_argv (const char *exec_file, + const std::string &allargs, + const char *shell_file) +{ + if (shell_file == NULL) + init_for_no_shell (exec_file, allargs); + else + init_for_shell (exec_file, allargs, shell_file); +} + +/* See declaration. */ + +void +execv_argv::init_for_shell (const char *exec_file, + const std::string &allargs, + const char *shell_file) +{ + const char *exec_wrapper = get_exec_wrapper (); + + /* We're going to call a shell. */ + bool escape_bang = escape_bang_in_quoted_argument (shell_file); + + /* We need to build a new shell command string, and make argv point + to it. So build it in the storage. */ + std::string &shell_command = m_storage; + + shell_command = "exec "; + + /* Add any exec wrapper. That may be a program name with arguments, + so the user must handle quoting. */ + if (exec_wrapper != NULL) + { + shell_command += exec_wrapper; + shell_command += ' '; + } + + /* Now add exec_file, quoting as necessary. */ + + /* Quoting in this style is said to work with all shells. But csh + on IRIX 4.0.1 can't deal with it. So we only quote it if we need + to. */ + bool need_to_quote; + const char *p = exec_file; + while (1) + { + switch (*p) + { + case '\'': + case '!': + case '"': + case '(': + case ')': + case '$': + case '&': + case ';': + case '<': + case '>': + case ' ': + case '\n': + case '\t': + need_to_quote = true; + goto end_scan; + + case '\0': + need_to_quote = false; + goto end_scan; + + default: + break; + } + ++p; + } + end_scan: + if (need_to_quote) + { + shell_command += '\''; + for (p = exec_file; *p != '\0'; ++p) + { + if (*p == '\'') + shell_command += "'\\''"; + else if (*p == '!' && escape_bang) + shell_command += "\\!"; + else + shell_command += *p; + } + shell_command += '\''; + } + else + shell_command += exec_file; + + shell_command += ' ' + allargs; + + /* If we decided above to start up with a shell, we exec the shell. + "-c" says to interpret the next arg as a shell command to + execute, and this command is "exec <target-program> <args>". */ + m_argv.reserve (4); + m_argv.push_back (shell_file); + m_argv.push_back ("-c"); + m_argv.push_back (shell_command.c_str ()); + m_argv.push_back (NULL); +} + +/* Return the shell that must be used to startup the inferior. The + first attempt is the environment variable SHELL; if it is not set, + then we default to SHELL_FILE. */ + +static const char * +get_startup_shell () +{ + static const char *ret; + + ret = getenv ("SHELL"); + if (ret == NULL) + ret = SHELL_FILE; + + return ret; +} + +/* See nat/fork-inferior.h. */ + +pid_t +fork_inferior (const char *exec_file_arg, const std::string &allargs, + char **env, void (*traceme_fun) (), + void (*init_trace_fun) (int), void (*pre_trace_fun) (), + const char *shell_file_arg, + void (*exec_fun)(const char *file, char * const *argv, + char * const *env)) +{ + pid_t pid; + /* Set debug_fork then attach to the child while it sleeps, to debug. */ + int debug_fork = 0; + const char *shell_file; + const char *exec_file; + char **save_our_env; + int i; + int save_errno; + + /* If no exec file handed to us, get it from the exec-file command + -- with a good, common error message if none is specified. */ + if (exec_file_arg == NULL) + exec_file = get_exec_file (1); + else + exec_file = exec_file_arg; + + /* 'startup_with_shell' is declared in inferior.h and bound to the + "set startup-with-shell" option. If 0, we'll just do a + fork/exec, no shell, so don't bother figuring out what shell. */ + if (startup_with_shell) + { + shell_file = shell_file_arg; + + /* Figure out what shell to start up the user program under. */ + if (shell_file == NULL) + shell_file = get_startup_shell (); + + gdb_assert (shell_file != NULL); + } + else + shell_file = NULL; + + /* Build the argument vector. */ + execv_argv child_argv (exec_file, allargs, shell_file); + + /* Retain a copy of our environment variables, since the child will + replace the value of environ and if we're vforked, we have to + restore it. */ + save_our_env = environ; + + /* Perform any necessary actions regarding to TTY before the + fork/vfork call. */ + prefork_hook (allargs.c_str ()); + + /* It is generally good practice to flush any possible pending stdio + output prior to doing a fork, to avoid the possibility of both + the parent and child flushing the same data after the fork. */ + gdb_flush_out_err (); + + /* If there's any initialization of the target layers that must + happen to prepare to handle the child we're about fork, do it + now... */ + if (pre_trace_fun != NULL) + (*pre_trace_fun) (); + + /* Create the child process. Since the child process is going to + exec(3) shortly afterwards, try to reduce the overhead by + calling vfork(2). However, if PRE_TRACE_FUN is non-null, it's + likely that this optimization won't work since there's too much + work to do between the vfork(2) and the exec(3). This is known + to be the case on ttrace(2)-based HP-UX, where some handshaking + between parent and child needs to happen between fork(2) and + exec(2). However, since the parent is suspended in the vforked + state, this doesn't work. Also note that the vfork(2) call might + actually be a call to fork(2) due to the fact that autoconf will + ``#define vfork fork'' on certain platforms. */ +#if !(defined(__UCLIBC__) && defined(HAS_NOMMU)) + if (pre_trace_fun || debug_fork) + pid = fork (); + else +#endif + pid = vfork (); + + if (pid < 0) + perror_with_name (("vfork")); + + if (pid == 0) + { + /* Close all file descriptors except those that gdb inherited + (usually 0/1/2), so they don't leak to the inferior. Note + that this closes the file descriptors of all secondary + UIs. */ + close_most_fds (); + + if (debug_fork) + sleep (debug_fork); + + /* Execute any necessary post-fork actions before we exec. */ + postfork_child_hook (); + + /* Changing the signal handlers for the inferior after + a vfork can also change them for the superior, so we don't mess + with signals here. See comments in + initialize_signals for how we get the right signal handlers + for the inferior. */ + + /* "Trace me, Dr. Memory!" */ + (*traceme_fun) (); + + /* The call above set this process (the "child") as debuggable + by the original gdb process (the "parent"). Since processes + (unlike people) can have only one parent, if you are debugging + gdb itself (and your debugger is thus _already_ the + controller/parent for this child), code from here on out is + undebuggable. Indeed, you probably got an error message + saying "not parent". Sorry; you'll have to use print + statements! */ + + restore_original_signals_state (); + + /* There is no execlpe call, so we have to set the environment + for our child in the global variable. If we've vforked, this + clobbers the parent, but environ is restored a few lines down + in the parent. By the way, yes we do need to look down the + path to find $SHELL. Rich Pixley says so, and I agree. */ + environ = env; + + char **argv = child_argv.argv (); + + if (exec_fun != NULL) + (*exec_fun) (argv[0], &argv[0], env); + else + execvp (argv[0], &argv[0]); + + /* If we get here, it's an error. */ + save_errno = errno; + warning ("Cannot exec %s", argv[0]); + + for (i = 1; argv[i] != NULL; i++) + warning (" %s", argv[i]); + + warning ("Error: %s\n", safe_strerror (save_errno)); + + _exit (0177); + } + + /* Restore our environment in case a vforked child clob'd it. */ + environ = save_our_env; + + postfork_hook (pid); + + /* Now that we have a child process, make it our target, and + initialize anything target-vector-specific that needs + initializing. */ + if (init_trace_fun) + (*init_trace_fun) (pid); + + /* We are now in the child process of interest, having exec'd the + correct program, and are poised at the first instruction of the + new program. */ + return pid; +} + +/* See nat/fork-inferior.h. */ + +ptid_t +startup_inferior (pid_t pid, int ntraps, + struct target_waitstatus *last_waitstatus, + ptid_t *last_ptid) +{ + int pending_execs = ntraps; + int terminal_initted = 0; + ptid_t resume_ptid; + + if (startup_with_shell) + { + /* One trap extra for exec'ing the shell. */ + pending_execs++; + } + + if (target_supports_multi_process ()) + resume_ptid = pid_to_ptid (pid); + else + resume_ptid = minus_one_ptid; + + /* The process was started by the fork that created it, but it will + have stopped one instruction after execing the shell. Here we + must get it up to actual execution of the real program. */ + if (get_exec_wrapper () != NULL) + pending_execs++; + + while (1) + { + enum gdb_signal resume_signal = GDB_SIGNAL_0; + ptid_t event_ptid; + + struct target_waitstatus ws; + memset (&ws, 0, sizeof (ws)); + event_ptid = target_wait (resume_ptid, &ws, 0); + + if (last_waitstatus != NULL) + *last_waitstatus = ws; + if (last_ptid != NULL) + *last_ptid = event_ptid; + + if (ws.kind == TARGET_WAITKIND_IGNORE) + /* The inferior didn't really stop, keep waiting. */ + continue; + + switch (ws.kind) + { + case TARGET_WAITKIND_SPURIOUS: + case TARGET_WAITKIND_LOADED: + case TARGET_WAITKIND_FORKED: + case TARGET_WAITKIND_VFORKED: + case TARGET_WAITKIND_SYSCALL_ENTRY: + case TARGET_WAITKIND_SYSCALL_RETURN: + /* Ignore gracefully during startup of the inferior. */ + switch_to_thread (event_ptid); + break; + + case TARGET_WAITKIND_SIGNALLED: + target_terminal_ours (); + target_mourn_inferior (event_ptid); + error (_("During startup program terminated with signal %s, %s."), + gdb_signal_to_name (ws.value.sig), + gdb_signal_to_string (ws.value.sig)); + return resume_ptid; + + case TARGET_WAITKIND_EXITED: + target_terminal_ours (); + target_mourn_inferior (event_ptid); + if (ws.value.integer) + error (_("During startup program exited with code %d."), + ws.value.integer); + else + error (_("During startup program exited normally.")); + return resume_ptid; + + case TARGET_WAITKIND_EXECD: + /* Handle EXEC signals as if they were SIGTRAP signals. */ + xfree (ws.value.execd_pathname); + resume_signal = GDB_SIGNAL_TRAP; + switch_to_thread (event_ptid); + break; + + case TARGET_WAITKIND_STOPPED: + resume_signal = ws.value.sig; + switch_to_thread (event_ptid); + break; + } + + if (resume_signal != GDB_SIGNAL_TRAP) + { + /* Let shell child handle its own signals in its own way. */ + target_continue (resume_ptid, resume_signal); + } + else + { + /* We handle SIGTRAP, however; it means child did an exec. */ + if (!terminal_initted) + { + /* Now that the child has exec'd we know it has already + set its process group. On POSIX systems, tcsetpgrp + will fail with EPERM if we try it before the child's + setpgid. */ + + /* Set up the "saved terminal modes" of the inferior + based on what modes we are starting it with. */ + target_terminal_init (); + + /* Install inferior's terminal modes. */ + target_terminal_inferior (); + + terminal_initted = 1; + } + + if (--pending_execs == 0) + break; + + /* Just make it go on. */ + target_continue_no_signal (resume_ptid); + } + } + + return resume_ptid; +} + +/* See nat/fork-inferior.h. */ + +void +trace_start_error (const char *fmt, ...) +{ + va_list ap; + + va_start (ap, fmt); + warning ("Could not trace the inferior process.\nError: "); + vwarning (fmt, ap); + va_end (ap); + + gdb_flush_out_err (); + _exit (0177); +} + +/* See nat/fork-inferior.h. */ + +void +trace_start_error_with_name (const char *string) +{ + trace_start_error ("%s: %s", string, safe_strerror (errno)); +} |